Dry sprinklers are used in areas that are exposed to freezing conditions, such as in freezers or walkways that may experience freezing conditions. In some dry-pipe systems supply conduits run in a space where the fluid in the supply conduit is not subject to freezing. A dry sprinkler is attached to the supply conduit and extends into a space where the fluid would otherwise be subject to freezing.
The typical construction of a dry sprinkler comprises a sprinkler head, a tube, a pipe connector at the inlet end of the tube (for connecting the inlet end to the pipe network of the fire suppression system), a plug seal at the inlet end to prevent water from entering the tube until it is necessary to actuate the sprinkler, and an actuating mechanism to maintain the plug seal at the inlet end until actuation. Typically, the sprinkler head is attached to the end of the tube opposite to the inlet end of the tube. Also, the tube is conventionally vented to the atmosphere to allow drainage of any condensate that may form in the tube.
Examples of dry sprinklers are generally disclosed in U.S. Pat. No. 5,775,431 to Ondracek and U.S. Pat. No. 5,967,240 to Ondracek. As shown generally in these patents, the actuating mechanism can be a rod or other similar structure that extends through the tube between the sprinkler head and the inlet end to maintain the seal at the inlet end. The actuating mechanism includes a thermally responsive support element at the sprinkler head that supports the rod and therefore the seal at the inlet end. In some sprinklers, the tube is also sealed at the sprinkler head end of the tube and the actuating mechanism is supported at the sprinkler head end by a seal cap supported by the thermally responsive support element. In such arrangements, the space in the tube between the two seal caps can be pressurized with a gas, such as dry air or nitrogen or with a liquid such as an antifreeze solution. When an elevated temperature is experienced, the thermally responsive support element fails releasing the plug seal (and also any lower seal at the sprinkler head end of the tube) to allow water from the supply conduit to flow into and through the tube to the sprinkler head, whereupon the fluid is distributed by the sprinkler head.
Conventional dry sprinklers are fabricated using a rigid tube having a seal at the inlet that is separated from the sprinkler's temperature sensor, which is intended to be positioned in an area exposed to freezing conditions, such as an area that is not heated. The rigid tube extends into the unheated area from a wet pipe system (located in a heated area) and must be precisely aligned and installed while avoiding various architectural, structural and mechanical obstructions typically found in commercial or industrial buildings.